A flat panel display such as a liquid crystal display is provided with an active device such as a thin-film transistor in each pixel to drive a display element. A method of driving such a type of display element is generally called an active matrix type driving. In the active matrix type driving, a thin-film transistor is embedded in each pixel to drive the corresponding pixel.
Meanwhile, a general thin-film transistor is formed by using amorphous silicon in a semiconductor layer. However, since amorphous silicon has a low electron moving velocity, it is difficult to implement high resolution and fast driving capability on an extra-large display screen. For this reason, an oxide thin-film transistor having electron moving velocity ten times faster than that of amorphous silicon has been developed. Recently, the oxide thin-film transistor is highlighted as a device capable of exhibiting ultra-high definition (UD) or higher resolution and a fast driving speed of 240 Hz or higher.
Typically, liquid crystal display devices are fabricated through photolithography. In the photolithography, a series of procedures including deposition of a patterning target material and a photoresist material, exposure using a mask, development of the photoresist, and etching are sequentially processed.
Recently, studies have been widely made for oxide semiconductors applicable in place of silicon-based semiconductor devices for the large-area display. In terms of material, some studies have resulted in feasible single-component, binary, or ternary compounds based on indium oxide (In2O3), zinc oxide (ZnO), and gallium oxide (Ga2O3). Meanwhile, in terms of process, studies have been made for a solution-based technique in place of existing vacuum deposition.
Although oxide semiconductors are also amorphous, they have very high mobility relative to hydrogenated amorphous silicon. Therefore, oxide semiconductors are suitable for high-quality liquid crystal devices (LCDs) and active matrix organic light emitting diodes (AMOLEDs). In addition, a technology of manufacturing an oxide semiconductor using a solution-based process is cost-effective while vacuum deposition techniques are expensive.
However, disadvantageously, oxide transistors fabricated using indium-zinc oxide (IZO) in the prior art are unstable from electrical and environmental viewpoints.